1. Field of the Invention
The present invention is directed to a gas laser having a cylindrical discharge envelope or tube, which consists of a glass casing, which is sealed at each of its two ends by metal end caps with a capillary being permanently secured adjacent one end cap and extending in the interior of the casing coaxially with at least one spring element supporting the free end of the capillary in the casing, a cold cathode surrounding at least the free end of the capillary and a portion thereof and connected to the other end cap, each of the end caps supporting tubular components which have weakened wall portions so that optical reflectors or mirrors secured on each of the tubular metal component to form an optical resonator can be easily adjusted.
2. Prior Art
Gas lasers of coaxial construction having an inner capillary have been known since approximately 1974. For example, a laser of this type was disclosed in an article by David L. Wright and Dale Crane, Electronics, June 13, 1974, pages 91-95. Another example is disclosed in U.S. Pat. No. 3,988,698 and a third example is disclosed in an article by Hans Golser, Helmut Kindl and Peter Maly, "Helium-Neon Laser Tube LGR 7621 of Coaxial Glass Technology", Components Report, Vol. XI, No. 1, March 1976, pages 1-4, which was published by Siemens Aktiengesellschaft. These gas lasers, which have the coaxial construction, have proven extremely successful on the market due to their rotational-symmetrical bodies which are completely smooth on the exterior and can be produced substantially automatically. Helium-neon lasers of this construction were previously, however, restricted to an output power of only a few mW and an increase of power could be achieved by only increasing the structural length of the laser tube. As a result of the development of heat during operation and when the plasma tube exceeds a critical length, the plasma tube is deflected or sags to such an extent that in a construction in which the capillary is inaccessible and cannot be subsequently corrected, the power must drop. Tube lengths of approximately 40 cm were previously assumed to exceed the critical value and in the casing a helium neon laser this length was synonymous with an output of approximately 7 mW.
In order to reach higher output powers, the general practice was to employ laser versions with external reflectors and thus designs from the earlier stages of the gas laser development, which had a considerably more complicated structure, for example, dust protection for the reflectors, Brewster windows, etc. It was previously attempted to retain the advantages of the inner capillary in the case of gas lasers having an increased output power of approximately 8 mW for a helium neon laser. Commercially available designs, for example, laser types LT-10 with a 10 mW output power and LT-15 with a 15 mW output power which were manufactured by CW Radiations Company, have however abandoned the cylindrical symmetry. For example, the cathode was located in an appendix vessel and the inner capillary consists of individual sections, which were each embraced by a glass support plate extending from the glass casing. It is obvious that this type of structure will also involve high production costs.
Thus, there was still lacking a cheap gas laser having a relatively high output power. Since there is a considerable continuously increasing requirement for "cheap lasers" having cylindrical symmetry, for example, for use as components in non-mechanical printers, this situation is particularly unsatisfactory.